Mechanical pneumatic delay timer

ABSTRACT

A mechanical pneumatic time delay device has an actuating arm attached to a piston located within a housing. A spring and a bellows for sealing the housing surrounds the actuating arm. A chamber within the housing adjacent the piston is filled with CO2 under pressure to compress the spring. A porous restrictor is positioned in a passageway in one wall of the housing. Support discs are provided on both sides of the restrictor. A puncture diaphragm is positioned adjacent the restrictor on the side remote from the pressure chamber. Puncture of the diaphragm initiates the time cycle.

United States Patent Inventors Jay N. l-lopps 72 2,689,916 9/1954 Lohman m1 l88/94X Minneapolis, Minn.; 2,697,538 12/1954 Seeler 222/5X Norman F. Green, Plymouth Village, Minn. 2,857,889 1958 Stott et al. l88/94X 211 Appl. No. 790,517 3,097,725 7/1963 Peterson 188/94 [22] Filed Jan. 9, 1969 3,375,908 4/l968 Chaput etal. 188/94 Patented May 11, 1971 Ex r Gem 6 E A Halv 731 Assignee the United States of America as represented g 9 by the g y o the Air Force Attorneys-Harry A. Herbert, Jr. and Richard J. Killoren [54] MECHANICAL PNEUMATIC DELAY TIMER l Chum 4 Drawing ABSTRACT: A mechanical pneumatic time delay device has [52] 11.8. CI 188/311, an actuating arm attached to a piston located within a housing. 267/151 A spring and a bellows for sealing the housing surrounds the [51] lnLCl .1; Fl6f 9/02 actuating arm. A chamber within the housing adjacent the Fleld'oisfiil'ch 188/94, piston is filled with CO2 under pressure to compress the 1005; 2 A spring. A porous restrictor is positioned in a passageway in one wall of the housing. Support discs are provided on both [56] References cued sides of the restrictor. A puncture diaphragm is positioned ad- UNITED STATES PATENT jacent the restrictor on the side remote from the pressure 2,103,378 l2/1937 Oestnaes et a1 188/94X chamber. Puncture of the diaphragm initiates the time cycle.

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MECHANICAL PNEUMATIC DELAY TIMER BACKGROUND or THE INVENTION- Time delay device of various types are known in the art for providing a time delay between the occurrence of two events. Such time delay devices may be electrical, chemical or mechanical. Some of the mechanical timers depend on the flow of a gas through a gas permeable membrane or container.

In some self-destruct systems, rugged-dependable long time delay timers are required. Pneumatic timers are known to be accurate for short time delays, but their accuracy is known to decrease when long time delays are required.

According to this invention a mechanical pneumatic time delay device is provided which is rugged in construction and which will operate within approximately :tl0.5 percent of the expected or designed time delay. A pressure chamber and a porous restrictor are provided wherein the initial pressure in the chamber and thickness of the restrictor determines delay time.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIG. I, of the drawing which shows a pneumatic time delay device having a housing 11 with a hollow cavity 12 therein. The cavity 12 has a portion 14 of smaller cross section than portion 16. The portions 14 and 16 may have a circular cross section, a rectangular cross section or other cross section. A passageway 18 having an enlarged portion 20 extends from hollow cavity 12 to the outside of the housing 10. A restrictor 22 is positioned in the enlarged portion 20 of passageway 18. A pair of restrictor supports 23 and 24, made for example of sintered copper, stainless steel or bronze, are positioned on either side of the restrictor 22. The restrictor may be made of a silicone rubber restrictor material, for example such as made by Dow Corning Corporation under the trade names Silastic 50" or Silastic I52".

Silastic 50 has been found to be more permeable to CO than Silastic 152". With a C0 gas pressure of 500 p.s.i.g. and a restrictor with a thickness of .025 inch, the flow rate was found to be 0.444 cc./min./in. for Silastic I52 and with the same pressure and thickness, the flow rate for Silastic 50" was found to be 6.73 cc./min./in.. For any particular restrictor material the flow rate is a function of the thickness of the restrictor material and the pressure of the gas. Therefore, the pressure of the CO in chamber 35 and the thickness of the restrictor may be selected to give the desired delay time for the particular restrictor material used.

A member 26, of a material such as aluminum, has a recess 28 machined therein to provide a thin puncture diaphragm 29. The diaphragm is scored in the usual manner to provide rapid breaking when hit by a puncture point 30 driven by a puncture projection 38 which extends through an opening in end cap 39 to operate a utilization device 50 as shown in FIGS. 2 and, 3. A spring 40 acts to urge the piston 36 toward chamber 35 to retract the plunger 37. A bellows 42 is sealed to piston 36 and end plate 39 to seal cavit 12 so that gas does not leak out around plunger 37. A rll tube 45 IS provided ad acent chamber 35.

In the operation of the device, the chamber 35 is filled with a gas such as CO to the pressure desired which for one device tested was 400 p.s.i. The device was allowed to soak for 1 hour after which the tube 45 was sealed off. The projection 38 then extends out of housing 10 to move operating rod 48 of a utilization device 50 to the position shown in FIG. 2. When the diaphragm 29 is perforated by means of a puncturing point 30 carried by a swinging or sliding member of a conventional design and operated by a mechanism 31, the gas leaks out through the restrictor 22 until the pressure in the chamber 14 drops to a pressure which permits the spring to move piston 36 to the left and retract projection 38 thus permitting the operating rod 48 to operate the utilization device 50, which may, for example, be a self-destruct mechanism or any other apparatus for which time delay operation is desired. The pressure at which spring 37 permits movement of the piston will be determined by the particular design, which for the design built was approximately 25 p.s.i.

FIG. 4 shows the delay time vs. restrictor thickness for a test unit where the gas in chamber 35 was CO at 400 p.s.i.g. Restrictor thicknesses from 0.0042 to 0.0099 inch were used for this test. The porous metal support discs were 0.055 inch thick.

Delay times of 51.3 hours have been achieved with a 0.1 inch restrictor with the initial pressure of the CO gas in chamber 35 at 400 p.s.i.g.

There is thus provided a dependable, rugged pneumatic delay timer for use where relatively 7 long delay times are desired.

We claim:

1. A time delay device comprising: a housing member; a

cylindrical cavity within said housing member; a piston forming onewall of a pressure chamber within said cavity; a plunger member extending through the wall of said housing; said plunger member being operatively connected to said piston; spring means, surrounding said plunger and engaging said piston for urging said plunger inwardly of said housing member; a gas under pressure within said pressure chamber for compressing said spring and for moving the end of said plunger in a direction away from the pressure chamber; means, surrounding said plunger and attached to said piston and said housing memberfor preventing the flow of gas around the plunger and out of said cavity; a gas passageway extending from said pressure chamber to the exterior of said housing; a frangible diaphragm sealing said passageway; means including a silicon rubber restrictor positioned in the passageway to restrict the flow of gas from said pressure chamber after said frangible diaphragm has been punctured; and a support means positioned on each side of the restrictor means. 

1. A time delay device comprising: a housing member; a cylindrical cavity within said housing member; a piston forming one wall of a pressure chamber within said cavity; a plunger member extending through the wall of said housing; said plunger member being operatively connected to said piston; spring means, surrounding said plunger and engaging said piston for urging said plunger inwardly of said housing member; a gas under pressure within said pressure chamber for compressing said spring and for moving the end of said plunger in a direction away from the pressure chamber; means, surrounding said plunger and attached to said piston and said housing member for preventing the flow of gas around the plunger and out of said cavity; a gas passageway extending from said pressure chamber to the exterior of said housing; a frangible diaphragm sealing said passagewaY; means including a silicon rubber restrictor positioned in the passageway to restrict the flow of gas from said pressure chamber after said frangible diaphragm has been punctured; and a support means positioned on each side of the restrictor means. 